The invention relates to a powder build unit, a corresponding device that comprises this powder unit, and a method that employs the powder build unit according to the invention.
Additive or generative manufacture is known under various names, most of which are trade names of machine manufacturers or research institutions. These names include selective laser melting (SLM), direct metal laser sintering (DMLS), laser powder bed (LPB), and laser cusing (laser beam melting).
The method includes the selective melting of a powder layer deposited on a platform by means of a laser or electron beam. Afterward, the platform is lowered and another powder layer is deposited. The method is repeated until an adequate number of layers have been formed in order to generate a complete three-dimensional object.
For deposition of the powder on the platform, a coater is moved transversely across the platform and pushes a mound of powder in front of it. The coater is at a certain distance from the preceding powder layer. Typically, doctor blades or brushes are employed as coaters. In these methods of manufacture based on powder beds, the surface roughness depends on, among other factors, the particle diameters. The smaller the particle size is, the lesser is the surface roughness of the manufactured component. However, a metal powder with smaller particle diameters is hygroscopic; that is, moisture, in particular water, from the surroundings is bound on the surfaces of the particles. As a result, the powder forms clumps and can no longer be distributed with a uniform thickness. Furthermore, additional energy is needed for the water present in the powder in order to melt the powder. However, this additional energy depends on the amount of bound water. This can lead to the fact that the powder completely melts in a locally dry region of a layer and the powder only partially melts in a locally moist region of the same layer. As a result of this, the layer is bonded to the preceding layer only in some regions. In the worst case, the partially manufactured component must be discarded.